Food-borne diseases are an important public health concern. In the United States alone, the occurrence of food-borne illness is estimated to be between 6 and 80 million illnesses with approximately 9000 deaths annually. The most prevalent agent causing food-borne illness is Campylobacter jejuni. This agent alone is estimated to be responsible for causing 4 million of these cases with more than 1000 deaths annually. Although less prevalent than Campylobacter jejuni, Salmonella (non-typhoid) is also a major health concern because it is responsible for 2 million cases of disease and approximately 2000 deaths each year. Further, more than 25,000 of these cases with more than 200 deaths annually have been attributed to food-borne Escherichia Coli 0157:H7. And while the incidence of disease due to E. Coli O157:H7 is much more rare than many other food-borne pathogens, such as Salmonella and Campylobacter, it is a particular concern because it is often life-threatening in children and the elderly.
Equally, in addition to the staggering health concerns associated with food-borne illness, is the severe economic burden these agents cause. This economic burden is not limited to one specific area of the economy, but stretches through several sectors. For example, human health costs associated with food-borne illness is estimated to be approximately 22 billion dollars annually in the United States alone. Equally devastating are the somewhat intangible costs incurred by the livestock industry, such as treatment costs and livestock deaths, negative public perception, increased cull rates, reduced feed efficiency, and decreased weight gain.
Animals have been identified as a major source of these food-borne illnesses when humans consume meat and other products contaminated with microorganisms at slaughter. In particular, the deadly food pathogen, E. coli O157:H7, is predominantly found in the intestinal tract of cattle. Food processors and government agencies have responded to this problem by instituting hazard analysis/critical control point (HACCP) models to provide food safety assurance. In fact, this program is required by the USDA in most meat and poultry processing facilities. HACCP systems are designed to systematically prevent food safety hazards from occurring. While HACCP has resulted in a decreased risk of contamination during the post-harvest period, it does not address the issue of contamination caused in the pre-harvest period.
Accordingly, there is growing consensus that control of food-borne pathogens in live animals is the most effective strategy for further reducing human food-borne illness. Toward that end, vaccination has been one approach employed to protect animals from carriage of microorganisms causing food-borne illness in humans. Vaccines, however, are not entirely effective in reducing the carriage of human, food-borne pathogens because many of these pathogens do not actually infect the animal, but merely reside in the animal's intestinal tract. As a result, vaccination is largely ineffective in preventing the slaughter-house contamination of meat intended for human consumption. Further diminishing the attractiveness of a vaccine based approach is the growing concern that the presence of antibiotic resistant genes in vaccines is resulting in the development of resistant populations of harmful bacteria.
Recently, the use of competitive exclusion products (“CEP”), such as probiotics, for inhibiting the carriage of food-borne pathogens in live animals has shown significant promise. Competitive exclusion employs the use of live microbial cultures that are not harmful to the animal and are also not harmful to humans. These microbial cultures are able to out compete food-borne pathogens in the animal's intestinal tract and prevent pathogens from colonizing. The use of a CEP based approach is thus promising, because unlike the vaccine based approach, CEPs are able to beneficially alter the microflora in the intestinal tract of the animal thereby reducing or eliminating the carriage of harmful human pathogens.
Probiotics, as discussed above, are an important class of CEP that have been reported to inhibit many food-borne pathogens including Escherichia coli, Campylobacter jejuni, Salmonella, and Listeria monocytogenes. Many classes of microorganisms are employed as probiotics including yeasts such as Saccharomyces and Torulopsis, fungi such as Aspergillus, and microorganisms belonging to the genera Bacillus and Clostridium have also been used.
Intestinal strains of lactic acid bacteria, however, are the most widely utilized class of microorganisms as probiotics. Lactic acid bacteria are widely employed as probiotics because members of this bacterial group are particularly suitable as antagonistic microorganisms in food due to their ability to inhibit other food-borne bacteria coupled with their ability to be used safely. For example, Nisbet et al. (U.S. Pat. No. 5,340,577) reported the reduction of Salmonella concentration in fowl using a probiotic mixture containing several lactic acid bacteria. Despite these advantages and successful use in fowl, however, lactic acid bacteria have not been employed as a means to reduce the carriage of food-borne pathogens in mature ruminant animals.
Accordingly, a need exists for a probiotic containing lactic acid bacteria effective in treating or preventing the carriage of food-borne pathogens in mature ruminant animals. The present invention addresses this need by providing strains of lactic acid bacteria that may be safely and economically employed as probiotics in mature ruminant animals.